The present invention relates to a piezoelectric transformer; and, more particularly, to a laminated piezoelectric transformer for use in such power sources as converters and inverters.
Piezoelectric transformers feature smaller sizes and easily obtainable higher efficiencies than conventional electromagnetic transformers. For such reasons, piezoelectric transformers are gaining popularity as step-up transformers, e.g., backlight power sources of liquid crystal display (LCD) monitors. However, step-down transformers are more frequently used in power supplies than step-up transformers.
It is preferable that a piezoelectric transformer have such characteristics as high output power, less heat generation, small size and higher efficiency. However, increasing the output power of a conventional piezoelectric transformer gives rise to the increased heat generation, which in turn reduces the output thereof.
Output power of a piezoelectric transformer is basically determined by a mechanical vibration velocity thereof. In order to obtain a high mechanical vibration velocity, it is preferable to construct an input (driving) part of a piezoelectric transformer to have a configuration capable of generating a large vibration.
Generation of large vibration can be achieved by constructing the electrodes in a laminated structure or by increasing the area of the electrodes. However, large vibrations in a piezoelectric transformer cause an increase in crystallographic and electric losses, resulting in an increased heat generation which in turn reduces the output power of the piezoelectric transformer.
It is, therefore, an object of the present invention to provide a piezoelectric transformer capable of obtaining large output powers by way of reducing the heat generation.
In accordance with the present invention, there is provided a piezoelectric transformer including: one or more input parts; and an output part, wherein each of the input parts is formed of alternately stacked piezoelectric sheets and internal electrodes and each piezoelectric sheet has a first region on which the internal electrode is formed and a second region on which no internal electrode is formed, and wherein each of the input parts includes means for reducing stress concentration around boundary regions between the first and the second regions.